Process for preparing vinylidene fluoride

ABSTRACT

Vinylidene fluoride is produced by the gaseous phase reaction of vinylidene chloride with at least 2 mols of hydrofluoric acid per mol of vinylidene chloride at a temperature of from 200* to 400*C. in presence of a catalyst selected from trivalent chromium salts and aluminum fluoride activated with a vanadium, tin or lanthanum compound.

United States Paten Kaess et al. 1 Mar. 27, 1973 s41 PROCESS FOR PREPARING 51 1m. 01 ..'.....c07 21/18 VINYLIDENE FLUORIDE Y [58] Field of Search ..260/653.3

[75] Inventors: Franz Kaess, Traunstein; Klaus 6 R f Lienhard, Trostberg-Mogling; Horst [5 1 e erences 'Michaud, Trostberg, all of Germany FOREIGN PATENTS 0R APPLICATION S |73| Assigncc: Suddeutsche Kalkqtickstoff-werkc 823,519 I H1959 (iltItl III-1min Jon/m I 1 Aktiengescllschafl, 'I'rnslhcrg 1,288,085 H1909 Germany ZOO/(v51. I Oberbayern, Germany v Primary ExaminerDaniel D. Horwitz [22] Filed 1971 Attorney-Christen, Sabol & OBrien [21] App]. No.: 171,023

ABSTRACT ted U.S. A D ta Rela ppihcauon a Vinylidene fluoride is produced by the gaseous phase [62] Division of Ser. No. 756,329, Aug. 29, I968. reaction of vinylidene chloride with at least 2 mols of hydrofluoric acid per mol of vinylidene chloride at a [30] Foreign Application Priority Data temperature of from 200 to 400C. in presence of a catalyst selected from trivalent chromium salts and aluminum fluoride activated with a vanadium, tin or lanthanum compound.

8 Claims, N5 Drawings PROCESS FOR PREPARING VINYLIDENE FLUORIDE This application is a division of application for U.S. Pat. Ser. NO. 756,329, filed Aug. 29, 1968.

This invention relates to the production of vinylidene fluoride by the fluorination of vinylidene chloride in the gaseous phase. p

Vinylidene fluoride has attained considerable im portance as a monomer for use in the production of homopolymers and copolymers. The homopolymers are especially useful for outside surface coatings and for chemical apparatus, because of their excellent resistance to atmospheric influences, chemicals and higher temperatures. The copolymers, especially those with trifluorochloroethylene or hexafluoropropylene, are elastomers having desirable characteristics, such as outstanding resistance to chemicals, high abrasion resistance and temperature stability.

Various methods have become known for the production of monomeric vinylidene fluoride. Processes which are based on the .elimination of hydrochloric acid from l,l,l-difluorochloroethane (German Patent No. 1,068,695) or hydrofluoric acid from l,l,1-trifluoroethane (US. Pat. No. 3,188,356) require starting materials that are difficult to obtain and relatively high temperatures, which in combination with the escaping halogen acids puts considerable demands on technology and apparatus. Moreover, such pyrolysis reactions have the disadvantage that a number of undesired by-products are often produced.

Further developments have been made due to the search for more readily available starting materials. Thus vinylidene fluoride can be produced, for example, by pyrolytic condensation of difluorochloromethane with methyl chloride (H. Mandai-R. Miller, J. prakt. chem. 19 (4), 202, 1963). The yields according to this process, however, are relatively low and the competing reaction of the formation of tetrafluoroethylerie from two molecules of difluorochloromethane is difficult to suppress.

Vinylidene chloride is a starting material that has' long been produced on a technical scale. However, previous attempts to produce vinylidene fluoride from this substance were carried out under intermittent pressure and saturated intermediate products had then to be converted in a second step through pyrolytic halogen acid elimination into vinylidene fluoride US. Pat. No. 2,637,747).

The process of the present invention for the production of vinylidene fluoride comprises reacting vinylidene chloride with hydrofluoric acid in a mol ratio of l 2 in a single reduction step in the gaseous phase at a temperature of 200-400C. in the presence of trivalent chromium salts previously heated to the reaction temperature under non-oxidizing conditions, or in the presence of aluminum fluoride activated with vanadium, tin or lanthanum.

The trivalent chromium salts may be deposited on a support, preferably activated carbon; Chromium salts which may be used include, for example, the chloride, bromide, fluoride, sulfate, nitrate, phosphate, formate and acetate. halogen A chromium salt-containing catalyst for fluorination and halide exchange reactions is described in U. S. Pat. No. 2,745,886. According to chemical analysis the catalyst has the formula 1 hits preparation from hydrated trivalent chromium fluoride an oxidizing pretreatment is essential, so that in the resultant catalyst, chromium of higher valence is present. This patented catalyst also differs substantially in its effect from the catalyst of the present invention. For example, it is not possible according to the patent to substitute fluorine for halogen atoms that are directly connected to a double bond carbon atom, unless chlorine or bromine is mixed with the unsaturated halogen hydrocarbon in the reaction with hydrofluoric acid. Consequently, however, only saturated fluorine containing compounds are obtained.

It is also known from German patent 1,000,798 to use aluminum fluoride with or without admixture with magnesium or copper or their halides as a ccatalystin the production of aliphatic fluorine compounds. This method is quite satisfactory for the reaction of saturated hydrocarbons, especially in the fluorination of carbon tetrachloride. In the reaction of unsaturated halogenated hydrocarbons with hydrofluoric acid, aside from halogen substitution, hydrofluoric acid addition must also take place, so that saturated flouridized hydrocarbons result.

With the catalysts of the present invention, a conversion to vinylidene fluoride of from 95 percent to more than 99 percent based on the vinylidene chloride introduced in the reaction is obtained. The total nonutilizable by-products, i.e., those which cannot by return to the process be converted to vinylidene fluoride, as CH CClF can be, amount in any case to less than 0.5 percent based on the vinylidene chloride introduced. in the process of the present invention, halogen exchange in the case ofvinylidene chloride thus succeeds selectively, i.e., with little or no addition of hydrofluoric acid to the double bond, so that in con -trast to known methods for producing vinylidene fluoride, an additional step for elimination of halogen acid is not necessary. In contrast, the results herein are unsatisfactorywhen aluminum fluoride is impregnated with compounds of cadmium, chromium, iron, manganese, molybdenum, nickel, zinc or zirconium.

The most favorable temperature range for the catalytic fluorination of vinylidene chloride according to the present invention is from 200 to 400C., preferably from 250' to 350C. At higher temperatures, the formation of by-products increases, while at lower temperatures the conversion decreases.

The reaction requires 2 mols of hydrofluoric acid per mol vinylidene chloride. It has been found advantageous, however, to use in addition an excess of hydrofluoric acid. Favorably molar ratios of vinylidene chloride to hydrofluoric acid are between 112.5 and 1:6, preferably between 1:35 and 125.5.

The space velocity is suitably adjusted to less than 500 N Ltr/h Ltr, (500 liters gaseous reaction mixture per hour catalyst charge volume in liters) N signifies normal conditions (pressure, temperature). The range of to 300 N Ltr/h Ltr has been found to be especially suitable.

Since the reaction proceeds without change in mol volume, the influence of pressure is of no importance. The process is therefore suitably conducted at normal pressure, particularly since increased pressure may lead to an increased formation of by-products, especially saturated compounds.

hydrous conditionand may be recycled into the reac- EXAMPLES 1 TO 7 150 grams CrCl .61-l O were slowly heated to 300C. in an evacuated glass flask connected to a running water jet pump until the initially dark green crystals changed into a solid violet porous mass. The mass after cooling was comminuted and screened to a particle size of from 2 .to 5 mm. Weight loss during the heating under vacuum amounted to 35 percent. 280 ml (81 grams) of the granulated catalyst were introduced into an iron pipe of 27 mm internal diameter and was brought to reaction temperature. A mixture of vinylidene chloride (VC and hydrofluoric acid (HF) was then passed through. The gases emerging from the reactor were washed with water and caustic soda solution, dried and condensed in condensers cooled with liquid nitrogen. The content of vinylidene fluoride (VF in the condensate was determined by gas chromatography. 7

The results obtained under various working conditions are shown in the following tables:

210 grams activated carbon with an averageparticle size of'2 mm was saturated with 400 ml of an aqueous solution of 65 grams chromium I trichloride (CrCl;,.61-1.0). The mixture was heated with stirring 'to 250C.for about 2 hours for the removal of the water.

The catalyst so obtained contained 4.1 percent by weight chromium.

The catalyst was placed in the same apparatus as in Examples .1-7, and a vaporous mixture of 1 part by volume vinylidene chloride and 3 parts by volume.

hydrofluoric acid was passed therethrough. The reaction temperature was 300C and the space velocity was 200 N Ltr/h Ltr. The vinylidene fluoride yield in mol percent based on the vinylidene chloride starting material was 98 percent.

' EXAMPLES 9 TO 11 acetic acid respectively.

150 grams activated carbon (particle size 2-3 mm) was introduced into each of three rotating tubes heated to 200300C and each impregnated by adding one of the freshly prepared trivalent chromium salt solutions. In this way the following catalysts were obtained:

CatalystA: Cr (SO activated carbon containing 2.9 percent Cr by weight Catalyst B: Cr(NO /activated 'carbon containing 2.8 percent Cr by weight Catalyst C: Cr(CH COO) /activated carbon containing 2.9 percent Cr by weight.

lneach case, 280 ml of one of these catalysts was placed in an iron pipe reactor (27 mm internal diameter) heated with a fused salt bath. Gaseous vinylidene chloride and hydrofluoric acid in a mol ratio of 1:4 and at a space velocity of N liters of the gaseous mixture per hour volume liter of catalyst charge were passed through the reactor at 340C. After removing the halogen acids by washing and drying, the gas mixture leaving the reactor was analyzed by gas chromatography.

The results are listed in the following table:

Yields of Fluorination I Activated AlF having a particle size of 2-3 mm was heated in a rotating tube to 200300C. and during rotation, aqueous La(NO solution was dropped in. The water evaporated immediately and the lanthanum compound was deposited on the surface of the AlF particles. The catalyst formed in this way contained 3.5 percent by weight of lanthanum. I

This catalyst was introduced into a pipe of standard steel with27 mrn internal diameter and heated in a fused salt bath to the reaction temperature measured in the center of the catalyst layer. A gaseousmixture of vinylidene chloride andhydrofluoric acid in a mol ratio 124.3 was passed through the catalyst layer at space velocity of N Ltr/h Ltr and a temperature of CH, CF, 96.0% CH, CFCl 0.8% Other by-products 0.2% Unreacted CH, CO, 3.0%

By distillation, vinylidene fluoride of 99.9 percent purity and having a boiling point of 82 to -8 1C. was recovered from the condensate. The compound was identified by its IR spectrum and the purity determined by gas chromatography. 5

Ltr.

EXAMPLE 13 In similar manner as in Example 12, by impregnating aluminum fluoride with an aqueous solution of ammonium vanadate, a catalyst was obtained containing 4.8 percent by weight vanadium.

In the apparatus described in Example 12, 1 volume part hydrofluoric acid was reacted on this catalyst with 3.5 volume parts vinylidene chloride at 330C. The space velocity of the reaction mixture was 1 N Ltr/h The reaction products obtained (in mol percent based on vinylidene chloride starting material) were CH,=CF, 94.6% CH,=CCIF 1.0% Other by-products 0.4% CH,=CCl, 4.0%

EXAMPLE l4 Other by products CH; =CCI, (unreacted) ratio of vinylidene chloride to hydrofluoric acid is between 1:25 and 1:6.

4. A process according to claim 3 wherein the mol ratio is between 123.5 and 125.5.

5. A process according to claim 1 wherein the gaseous mixture of vinylidene'chloride and hydrofluoric acid is passed over the catalyst at a space belocity below 500 N. Ltr/h.Ltr.

6. A process according to claim 5 wherein the space velocity is from to 300 N. Ltr./h. Ltr.

7. A process according to claim 1 wherein the reactionis carried out at atmospheric pressure.

8. A process according'to claim 1 wherein-the reaction is carried out in a continuous manner. 

2. A process according to claim 1 wherein the reaction is carried out at a temperature between 250* and 350*C.
 3. A process according to claim 1 wherein the mol ratio of vinylidene chloride to hydrofluoric acid is between 1:2.5 and 1:
 6. 4. A process according to claim 3 wherein the mol ratio is between 1:3.5 and 1:5.5.
 5. A process according to claim 1 wherein the gaseous mixture of vinylidene chloride and hydrofluoric acid is passed over the catalyst at a space belocity below 500 N. Ltr/h.Ltr.
 6. A process according to claim 5 wherein the space velocity is from 100 to 300 N. Ltr./h. Ltr.
 7. A process according to claim 1 wherein the reaction is carried out at atmospheric pressure.
 8. A process according to claim 1 wherein the reaction is carried out in a continuous manner. 